Assembly processes inferred from eDNA surveys of a pond metacommunity are consistent with known species ecologies
Abstract
Technological advances are enabling ecologists to conduct large‐scale and structured community surveys. However, it is unclear how best to extract information from these novel community data. We metabarcoded 48 vertebrate species from their eDNA in 320 ponds across England and applied the ‘internal structure' approach, which uses joint species distribution models (JSDMs) to explain compositions as the result of four metacommunity processes: environmental filtering, dispersal, species interactions, and stochasticity. We confirm that environmental filtering plays an important role in community assembly, and find that species' estimated environmental preferences are consistent with known ecologies. We also detect negative biotic covariances between fish and amphibians after controlling for divergent environmental preferences, consistent with predator–prey interactions (likely mediated by predator avoidance behaviour), and we detect high spatial autocorrelation for the palmate newt, consistent with its hypothesised relict distribution. Promisingly, ecologically and spatially distinctive sites are better explained by their environmental covariates and geographic locations, respectively, revealing sites where environmental filtering and dispersal limitation act more strongly. These results are consistent with the recent proposal that applying JSDMs to species distribution patterns can help reveal the relative importance of environmental filtering, dispersal limitation, and biotic interaction processes for individual sites and species. Our results also highlight the value of the modern interpretation of metacommunity ecology, which embraces the fact that assembly processes differ among species and sites. We discuss how novel community data allow for several study design improvements that will strengthen the inference of metacommunity assembly processes from observational data.
What the paper shows and why it matters
(AI-generated)
Metacommunity theory explains which species occur where through four forces: environmental filtering, dispersal, interactions between species and chance. Early work tended to study subsets of these forces, which gave rise to four idealised paradigms, although no real metacommunity (a set of local communities linked by dispersal) follows any one of them alone. Summary measures such as alpha and beta diversity (diversity within and between sites) cannot show how strongly each force acts on individual species and sites. Leibold et al. (2022) therefore proposed reading the “internal structure” of a metacommunity from a joint species distribution model (a statistical model that fits all species at once). This splits the pattern of each species and each site into environmental, spatial and biotic-covariance parts (shared patterns that neither environment nor location explain), and they tested the idea on simulated communities. What remained open was how best to apply this to the novel community data, such as eDNA surveys, that were becoming available.
The study tests the “internal structure” approach, which reads assembly processes from a joint species distribution model, on a real system of pond vertebrates, and argues that it gives plausible, informative results: assembly processes differ among species and among sites, and the inferred patterns agree with what is known about the species, rather than one paradigm describing the whole system. As its test case, the study uses environmental DNA (DNA that animals shed into their surroundings) from 320 English ponds, with 48 vertebrate species. Environmental filtering emerged as an important force, and the estimated environmental preferences of species were consistent with their known ecologies. Fish and amphibians showed negative biotic covariances, which fits predation. The palmate newt’s distribution was strongly spatially structured, which fits its suggested relict distribution.
The results suggest that ideas from metacommunity theory can be checked on observational survey data, by comparing the environmental, spatial and covariance components with independent knowledge of the species. The question for a system then becomes how much each process matters for which species and sites, rather than which single paradigm applies. The evidence is consistency with known ecology, not direct proof of the processes. The study also discusses how study designs enabled by new kinds of community data could strengthen such inference.
References
- Leibold et al. (2022). The internal structure of metacommunities. Oikos 2022, oik.08618. doi:10.1111/oik.08618